A number of systems for converting sunlight to electricity are known. One such system that has proven useful in efficiently producing electricity from the sun's radiation is described in U.S. Pat. No. 4,691,076. In that system, an array is formed of semi-conductor spheres. Each sphere has a P-type interior and an N-type skin. A plurality of the spheres are housed in a pair of aluminum foil members which form the contacts to the P-type and N-type regions. The foils are electrically insulated from one another and are flexible. Multiple arrays can be interconnected to form a module of solar cell elements for converting sunlight into electricity.
In order to produce sufficient quantities of the arrays, it is necessary to have a process for their manufacture that is uncomplicated, low cost and efficient. An uncomplicated system would be one using currently available technology constructed in such a way that the applicable process steps can be conducted in a highly repeatable manner. Moreover, the less complicated the process steps, generally the more cost effective will the entire process be carried out. Finally, the more repeatable the process, the more efficiently the operation and the higher production of solar arrays.
A key process step in the making of silicon solar cells is forming good ohmic contact between the P-type region of the silicon sphere and the foil forming the back bond. The only known technique for bonding the backfoil to the silicon spheres is to apply an insulating coat, then remove a portion of the coat from the sphere tips and apply the backfoil directly to the spheres. This technique was labor intensive and very dependent upon the individual operator. Another problem with the technique was that it was difficult to obtain good ohmic contact between the silicon sphere and the backfoil when the back foil is bonded at temperatures in the range of 300.degree. C. to 350.degree. C. Still another difficulty with the technique was that it did not lend itself to methods of mass production.